Amino acid polymers too short to fold up like proteins.
Amino acids are building blocks for proteins.
And these proteins need to fold up to fulfill its function (like sight, muscle, taste, etc)
However, if the polymer chain is too short, it becomes a peptide.
Enzyme is a protein that perform catalysis.
Polymers are large molecules in terms of number of atoms compared to say H2O.

Ramblings between my best friend and I about peptides.